SEX DIFFERENTIATION
• Although, sex of embryo is determined genetically at time of fertilization,
gonads do not differentiate until 7th week of development after arrival of
primordial germ cells into the indifferent gonad.
• If embryo is genetically male (primordial germ cells carry XY sex chromosome);
indifferent gonad differentiates into testis.
• If embryo is genetically female (primordial germ cells carry XX sex
chromosome):
indifferent gonad differentiates into ovary.
• When primordial germ cells fail to reach indifferent gonad, gonad remains
indifferent or is absent.
SEX DIFFERENTIATION IN MALES
• SRY gene on Y chromosome is master gene for testis development.
• SRY induces differentiation of Sertoli & Leydig cells.
***Sertoli cells secrete Mullerian inhibiting substance (MIS) which causes
regression of paramesonephric ducts.
***Leydig cells secrete Testosterone which causes differentiation of mesonephric
ducts & male external genitalia.
• Although, sex of embryo is determined genetically at time of fertilization,
gonads do not differentiate until 7th week of development after arrival of
primordial germ cells into the indifferent gonad.
• If embryo is genetically male (primordial germ cells carry XY sex chromosome);
indifferent gonad differentiates into testis.
• If embryo is genetically female (primordial germ cells carry XX sex
chromosome):
indifferent gonad differentiates into ovary.
• When primordial germ cells fail to reach indifferent gonad, gonad remains
indifferent or is absent.
SEX DIFFERENTIATION IN MALES
• SRY gene on Y chromosome is master gene for testis development.
• SRY induces differentiation of Sertoli & Leydig cells.
***Sertoli cells secrete Mullerian inhibiting substance (MIS) which causes
regression of paramesonephric ducts.
***Leydig cells secrete Testosterone which causes differentiation of mesonephric
ducts & male external genitalia.
